<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>0</h1>
<script>
    let count = 0;
    //开启定时器,将方法作物参数进行传递时不加(),调用方法时加()
    setInterval(f, 10);
    function f() {
        count++;
        let h = document.querySelector('h1');
        h.innerText = count;
    }
    //匿名方法开始定时器
    let timer = setInterval(function () {
        console.log(count);
        if (count >= 300) {
            //停止定时器
            clearInterval(timer);
        }
    }, 1000);
    //开启只执行一次的定时器
    setTimeout(function () {
        console.log("时间到!");
    }, 2000);
</script>
</body>
</html>